Flavour symmetry breaking in the kaon parton distribution amplitude
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Date
2014
Authors
Shi, C.
Chang, L.
Roberts, C.
Schmidt, S.
Tandy, P.
Zong, H.
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Physics Letters B: Nuclear Physics and Particle Physics, 2014; 738:512-518
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Chao Shi, Lei Chang, Craig D. Roberts, Sebastian M. Schmidt, Peter C. Tandy, Hong-shi Zong
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Abstract
We compute the kaon’s valence-quark (twist-two parton) distribution amplitude (PDA) by projecting its Poincaré-covariant Bethe–Salpeter wave-function onto the light-front. At a scale ζ = 2GeV, the PDA is abroad, concave and asymmetric function, whose peak is shifted 12–16% away from its position in QCD’s conformal limit. These features are a clear expression of SU(3)-flavour-symmetry breaking. They show that the heavier quark in the kaon carries more of the bound-state’s momentum than the lighter quark and also that emergent phenomena in QCD modulate the magnitude of flavour-symmetry breaking: it is markedly smaller than one might expect based on the difference between light-quark current masses. Our results add to a body of evidence which indicates that at any energy scale accessible with existing or foreseeable facilities, a reliable guide to the interpretation of experiment requires the use of such nonperturbatively broadened PDAs in leading-order, leading-twist formulae for hard exclusive processes instead of the asymptotic PDA associated with QCD’s conformal limit. We illustrate this via the ratio of kaon and pion electromagnetic form factors: using our nonperturbative PDAs in the appropriate formulae, Fk/Fπ=1.23 at spacelike-Q2=17 GeV2, which compares satisfactorily with the value of 0.92(5) inferred in e+e− annihilation at s=17 GeV2.
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© 2014 Argonne National Laboratory and the authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/ . Funded by SCOAP3.